Since Carothers early work in the 1920s and 1930s, aromatic polyester particularly poly(ethylene terephthalate) have become the most commercial important polyesters. The usefulness of these polymers is intimately linked to the stiffening action of the p-phenylene group in the polymer chain. The presence of the p-phenylene group in the backbone of the polymer chain leads to high melting points and good mechanical properties especially for fibers, films and some molded products. In fact poly(ethylene terephthalate) has become the polymer of choice for many common consumer products, such as one and two liter soft drink containers.
Several related polyester resins have been described in U.S. Pat. Nos. 4,440,922, 4,552,948 and 4,963,641 which seek to improve upon the properties of poly(ethylene terephthalate) by replacing terephthalic acid with other related dicarboxylic acids which contain phenylene groups. These polymers are generally designed to reduce the gas permeability of aromatic polyesters.
Other aromatic polyesters have also been developed for specialty applications such as radiation stable bioabsorbable materials. U.S. Pat. Nos. 4,510,295, 4,546,152 and 4,689,424 describe radiation sterilizable aromatic polyesters, which can be used to make sutures and the like. These polymers like, poly(ethylene terephthalate), have phenylene groups in the backbone of the polymers.
However, less research has been reported on aliphatic polyesters. After Carothers initial work on polyesters, aliphatic polyesters were generally ignored because it was believed that these materials had low melting points and high solubilities. The only aliphatic polyesters that have been extensively studied are polylactones such as polylactide, polyglycolide, poly(p-dioxanone) and polycaprolactone. These aliphatic polylactones have been used primarily for bioabsorbable surgical sutures and surgical devices such as staples. Although polylactones have proven to be useful in many applications they do not meet all the needs of the medical community. For example films of polylactones do not readily transmit water vapor, therefore, are not ideally suited for use as bandages where the transmission of water vapor would be desired.
Recently there has been renewed interest in non-lactone aliphatic polyesters. U.S. Pat. No. 5,349,028 describes the formation of very simple aliphatic polyesters based on the reaction of a diol with a dicarboxylic acid to form prepolymer chains that are then coupled together. These polyesters are being promoted for use in fibers and molded articles because these polyesters are biodegradable after they are buried such as in a landfill. However, these materials are not disclosed as being suitable for use in surgical devices.
To address the deficiencies in the polymers described in the prior art we invented a new class of polymers which are disclosed in U.S. Pat. Nos. 5,464,929; 5,595,751; 5,597,579; 5,607,687; 5,618,552; 5,620,698; 5,645,850; 5,648,088; 5,698,213; and 5,700,583 (all of which are hereby incorporated by reference). This new class of polymer are hydrolyzable and suitable for a variety of uses including medical applications. To further broaden the possible uses for these polymers we are disclosing and claiming herein copolymers of the polyoxaesters containing amines and/or amido groups and blends thereof with other polymers with modified hydrolysis profiles. These polymers may be used in a variety of applications where biodegradable polymers are desirable, as well as, in medical devices.